While it may be accurate to say that a majority of the American public has "moved on" with regard to marriage equality, that's not true among the base of the GOP. And, more critically, the majority of Americans in general hasn't "moved on" when it comes to "religious liberty" vs. "gay rights," not by a long shot.
Voteres want a president who is experienced, well-versed and firm on dealing with the inevitable crises that will confront the country. There's absolutely no hint that the general public has shut down on Clinton in this vital area of public policy. But this won't stop the GOP from peddling that line.